AB0556 CHARACTERISTICS OF PATIENTS DIAGNOSED WITH UNDIFFERENTIATED CONNECTIVE TISSUE DISEASE
Authors: C. Siegel, B. Stamm, J. Vega, E. Sevim, M. Lockshin, L. Sammaritano, M. Barbhaiya
Journal: Annals of the Rheumatic Diseases (2022)

Background Patients with undifferentiated connective tissue disease (UCTD) struggle with physical symptoms as well as diagnostic uncertainty. 1 UCTD diagnosis requires exclusion of other connective tissue diseases (CTD). Prior studies use variable definitions of UCTD that do not account for updated classification criteria thus limiting generalizability. Objectives We identified characteristics associated with rheumatologist-diagnosed UCTD, applied strict exclusion criteria, and compared UCTD patients to those with criteria-defined CTD. Methods We recruited patients ≥18 years old seen between 2018-2022 who had rheumatologist-diagnosed UCTD with positive ANA and ≥1 sign/symptom of a CTD. We reviewed medical records to identify those who fulfilled ACR/EULAR-endorsed classification criteria for SLE, RA, SSc, Primary Sjögren’s, Idiopathic Inflammatory Myopathy, and 2006 Revised Sapporo Criteria for APS. We compared sociodemographic, clinical, serologic, and treatment variables between UCTD and CTD using chi-square, Fisher’s exact, and t-tests. Results Of 89 patients with rheumatologist-diagnosed UCTD (mean age 49.0 ± 13.7 years, 97.8% female, 66.3% White), 59 (66.3%) had UCTD and 30 (33.7%) had criteria-defined CTD (27 SLE, 3 SLE and RA, 1 RA, and 1 APS). Patients in both groups had similar non-criteria manifestations, most commonly arthralgia (89.8% UCTD vs. 83.3% CTD, p=0.50) and fatigue (55.9% UCTD vs. 73.3% CTD, p=0.17). Compared to patients with CTD, those with UCTD were less likely to have nonerosive arthritis (27.1% vs. 56.7%, p=0.01) (Table 1). Table 1. Characteristics of Patients with UCTD or Criteria-Defined CTD UCTD 1 (n=57), N (%) CTD 2 (n=32), N (%) p-values Clinical 3,4 •,4nicalN (%))cs of Pa 16 (27.1) 17 (56.7) 0.01 •.0156.7) (%))cs of Patients with UCTD or Criteria 31 (52.5) 18 (60.0) 0.65 •.6560.0) (%))cs of Patient 7 (11.9) 4 (13.3) 1.0 •.013.3)) (%))cs of Patients with UCTD or Criteria-Defined C 27 (45.8) 14 (46.7) 1.0 •.0(46.7) (%))cs of Patien 24 (40.7) 11 (36.7) 0.82 Serology 3 •erology) (%))cs of Patients with UCTD or Criteria-Defined CTDth 19 (32.2) 19 (63.3) &lt;0.01 •0.013.3) (%))cs of Patien 9 (15.3) 13 (4.3) &lt;0.01 •0.01.3)) (%)) 22 (37.3) 25 (83.3) &lt;0.01 •0.013.3) (%))cs of Patients w 10 (16.9) 6 (20.0)) 0.77 •.770.0)) (%))cs of Patients with UCTD or Criteria-D 6 (10.2) 2 (6.7) 0.71 •.71.7))) (%))cs of Patients with UCTD or Criteria-Defined CTDther CTDs. Our fi 18 (30.5) 10 (33.3) 0.81 •.8133.3) (%))cs 11 (18.6) 6 (20.0) 1.0 1. Do not fulfill ACR/EULAR classification criteria for SLE, RA, SSc, PSS, IIM, APS. 2. Diagnosed with UCTD and fulfill ≥1 set of listed CTD classification criteria. 3. Defined per listed classification criteria 4. Criteria with n≤5: fever, proteinuria/cellular casts, pulmonary hypertension, interstitial lung disease, dysphagia/esophageal dysmotility Patients with UCTD were less likely than those with CTD to have any hematologic manifestation (lymphopenia, leukopenia, thrombocytopenia, or hemolytic anemia) (p=0.02), anti-dsDNA or anti-Smith antibodies (p&lt;0.01), or hypocomplementemia (p&lt;0.01). The frequency of RA, Sjogren’s, and APS-related serologies did not differ between groups (Table 1 ). Compared to those with CTD, UCTD patients were less likely to have ever received systemic corticosteroids (71.2% vs. 96.7%, p&lt;0.01); ever use of any disease-modifying antirheumatic drug (DMARD) was similar (35.6% vs. 46.7%, p=0.36). Conclusion Among patients diagnosed with UCTD, 66.3% met a stringent definition. Compared to those with criteria-defined CTD, UCTD patients had lower frequency of arthritis, hematologic abnormalities, SLE-specific antibodies, and hypocomplementemia. While use of DMARDs did not differ, UCTD patients were less likely to use systemic corticosteroids. Rheumatologists diagnose UCTD even when criteria are met for other CTDs. Our findings suggest UCTD is nonetheless a distinct clinical entity; more rigorous characterization will enable generalizable prognostic and therapy trials. References [1]Siegel CH, et al. J Clin Rheumatol 2021 Mar 5. doi: 0.1097/RHU. 0000000000001714 Disclosure of Interests None declared